Recently, from the viewpoint of depletion of fossil resources and measures against global warming, a shift to a manufacturing process of chemical goods using renewable resources (so-called bio-refinery) has been required. In particular, the application of various organic acids which can be efficiently obtained biochemically from biomass has been widely studied as the next-generation chemical block. For example, hydroxycarboxylic acids are a useful compound not only as a synthesis material of fine organic chemicals but also as a monomer unit of polyhydroxyalkanoic acid (PHA), as a bio-polyester which is known as being produced by the accumulation in microorganisms. In particular, poly-3-hydroxybutanoic acid which is a typical PHA derived from microorganisms attracted attention to its property as a biodegradable polymer mainly in 1980-1990's and a vigorous attempt has been made for the elucidation of the biosynthetic pathway and the productivity improvement. Recently, the potential of 3-hydroxybutanoic acid being a structure unit of poly-3-hydroxybutanoic acid as a chemical block has been attracting attention again, and various biochemical methods of producing a 3-hydroxybutanoic acid monomer have been proposed.
Specifically, the methods as follows are known:                a method of extracting poly-3-hydroxybutanoic acid accumulated in the microbial cell body and hydrolyzing it by the action of the enzyme or microorganism having degradation activity to obtain (R)-3-hydroxybutanoic acid as being a monomer unit (Non-patent Document 1);        a method of allowing high expression in vivo of poly-3-hydroxybutanoic acid depolymerase in poly-3-hydroxybutanoic acid-producing bacteria and sequentially degrading the generated 3-hydroxybutanoic acid oligomer to obtain (R)-3-hydroxybutanoic acid during the culture period (Non-patent Document 2);        a method of eliminating CoA by the conjugate with phosphorylation by allowing coexpressed phosphotrans butyrylase (ptb) and butyrate kinase (buk) to act sequentially on 3-hydroxybutyryl CoA in vivo as being a precursor of 3-hydroxybutanoic acid to obtain (R)-3-hydroxybutanoic acid during the culture period (Non-patent Document 3); and        a method of eliminating CoA by allowing coexpressed thiolase to act sequentially on 3-hydroxybutyryl CoA to obtain (R)-3-hydroxybutanoic acid during the culture period (Non-patent Document 4).        